Melt butter or oil in a large pan. Add onions, and sweat over a medium heat until transparent, stirring. Do not let them brown. Add apple, cinnamon, thyme, stock and cider. Bring back to boiling point and simmer for about 30 minutes, covered.

Allow to cool. If you used fresh thyme, remove the sprigs. Use a blender to puree the soup, leaving about 1/2 cup unpureed to stir through the rest (if you want people to know it was home-made).